Potential detecting circuit

Abstract

An object of the present invention is to enable detection of a precise substrate potential even when the substrate potential of the detecting circuit is at a lower level than the substrate to be measured, and to allow free setting of the stable detection level without being affected by fluctuation in the power supply potential. To that end, there are provided an operational amplifier for differential amplification when the ground potential and the positive power supply potential are supplied, a first resistor for transmitting the substrate potential to the first input terminal of the operational amplifier, a constant voltage circuit, and a reference voltage generating circuit for supplying a positive reference voltage to the second input terminal of the operational amplifier.

What is claimed is: 
     
       1. A potential-detecting circuit comprising a differential amplifier means having first and second input terminals for enabling a differential operation and a third terminal for giving an output of the differential result, a first resistor having one end connected to a substrate to be measured, a constant voltage generating means having a low potential side connected to a second end of said first resistor and having a high potential side connected to said first input terminal of the differential amplifier means, a reference voltage generating means for supplying a positive reference voltage to said second input terminal of the differential amplifier means, and a second resistor connected between said third output terminal and said first input terminal of the differential amplifier means. 
     
     
       2. A potential-detecting circuit comprising first reference voltage generating means for supplying a reference voltage, second reference voltage generating means for supplying a positive reference voltage which is lower than said first reference voltage, a first potential-detecting means for discriminating the potential of a substrate to be measured with respect to said first reference voltage, a second potential-detecting means for discriminating said potential of said substrate with respect to said second reference voltage, and an output means for emitting the result of said first potential-detecting means when said potential of said substrate becomes higher than said first reference voltage and emitting the result of said second potential-detecting means when said potential of said substrate becomes lower than said second reference voltage.